Pressure sensors are used in a wide range of industrial and consumer applications. Pressures of many different magnitudes may be measured using various types of pressure sensors, such as Bourdon-tube type pressure sensors, diaphragm-based pressure sensors and piezoresistive pressure sensors on silicon or silicon on insulator (SOI). Several variations of the diaphragm-based pressure sensor have been utilized to measure different ranges of pressure, such as by utilizing cantilever-based pressure sensors, optically read pressure sensors and the like.
Fiber optic sensors utilizing a Fabry-Perot cavity have been demonstrated to be attractive for the measurement of temperature, strain, pressure and displacement, due to their high sensitivity. The major advantages of fiber optic sensors over conventional electrical sensors include immunity to electromagnetic interference (EMI), compatibility with harsh environments and potential for multiplexing.
Microelectro-mechanical systems (MEMS) fabrication techniques make Fabry-Perot sensors more attractive by the potential precision in achieving specific Fabry-Perot cavity depths, diaphragm thicknesses, and diameters. This reduces potential yield loss from “out of specification” parts and reduces the necessary accuracy of the interrogation optics. In comparison to electronic high temperature pressure sensors, Fabry-Perot optical sensors are ideal for use in harsh environments because they do not require electronics to be located in the high temperature, harsh environment. Typically, a piezoresistive or piezoelectric pressure sensor require electronics to be located in close proximity to reduce noise by amplifying the signal. At temperatures greater than 200° C., commercially available high temperature electronics are not available limiting the use of these sensors due to poor signal to noise ratios. For a Fabry Perot optical sensor, the electronics and optics for reading and converting the optical signal to an output voltage can be located in a cool region, allowing the use of commercially available components which can enable reduced cost and high accuracy.
Fiber optic sensors are also of great interest for application in avionics and aerospace applications because their immunity to EMI provides significant weight savings through the elimination of cable shielding and surge protection electronics. In the biomedical field, fiber optic sensors have also proven successful resulting from their reliability, biocompatibility and the simplicity of the sensor-physician interface.